searx: add query_suffix parameter

- allows to build tools and dynamically inject extra searxh suffix in
  the query
 example: search.run("python library", query_suffix="site:github.com")
 resulting query: "python library site:github.com"

langchain/utilities/searx_search.py

@@ -78,6 +78,28 @@ For example the following query:
         # or even:
         s = SearxSearchWrapper("langchain library !gh")
 
+
+In some situations you might want to pass an extra string to the search query.
+For example when the `run()` method is called by an agent. The search suffix can
+also be used as a way to pass extra parameters to searx or the underlying search
+engines.
+
+    .. code-block:: python
+
+        # select the github engine and pass the search suffix
+        s = SearchWrapper("langchain library", query_suffix="!gh")
+
+
+        s = SearchWrapper("langchain library")
+        # select github the conventional google search syntax
+        s.run("large language models", query_suffix="site:github.com")
+
+
+*NOTE*: A search suffix can be defined on both the instance and the method level.
+The resulting query will be the concatenation of the two with the former taking
+precedence.
+
+
 See `SearxNG Configured Engines
 <https://docs.searxng.org/admin/engines/configured_engines.html>`_ and
 `SearxNG Search Syntax <https://docs.searxng.org/user/index.html#id1>`_
@@ -128,12 +150,15 @@ class SearxResults(dict):
 
     @property
     def results(self) -> Any:
-        """Silence mypy for accessing this field."""
+        """Silence mypy for accessing this field.
+
+        :meta private:
+        """
         return self.get("results")
 
     @property
     def answers(self) -> Any:
-        """Accessor helper on the json result."""
+        """Helper accessor on the json result."""
         return self.get("answers")
 
 
@@ -171,6 +196,7 @@ class SearxSearchWrapper(BaseModel):
     params: dict = Field(default_factory=_get_default_params)
     headers: Optional[dict] = None
     engines: Optional[List[str]] = []
+    query_suffix: Optional[str] = ""
     k: int = 10
 
     @validator("unsecure")
@@ -232,13 +258,15 @@ class SearxSearchWrapper(BaseModel):
         self._result = res
         return res
 
-    def run(self, query: str, engines: List[str] = [], **kwargs: Any) -> str:
+    def run(self, query: str, engines: List[str] = [],
+            query_suffix: str = "", **kwargs: Any) -> str:
         """Run query through Searx API and parse results.
 
         You can pass any other params to the searx query API.
 
         Args:
             query: The query to search for.
+            query_suffix: Extra suffix appended to the query.
             engines: List of engines to use for the query.
             **kwargs: extra parameters to pass to the searx API.
 
@@ -251,12 +279,21 @@ class SearxSearchWrapper(BaseModel):
                 searx = SearxSearchWrapper(searx_host="http://my.searx.host")
                 searx.run("what is the weather in France ?", engine="qwant")
 
+                # the same result can be achieved using the `!` syntax of searx
+                # to select the engine using `query_suffix`
+                searx.run("what is the weather in France ?", query_suffix="!qwant")
         """
         _params = {
             "q": query,
         }
         params = {**self.params, **_params, **kwargs}
 
+        if len(self.query_suffix) > 0:
+            params["q"] += " " + self.query_suffix
+
+        if isinstance(query_suffix, str) and len(query_suffix) > 0:
+            params["q"] += " " + query_suffix
+
         if isinstance(engines, list) and len(engines) > 0:
             params["engines"] = ",".join(engines)
 
@@ -274,13 +311,16 @@ class SearxSearchWrapper(BaseModel):
         return toret
 
     def results(
-        self, query: str, num_results: int, engines: List[str] = [], **kwargs: Any
+        self, query: str, num_results: int, engines: List[str] = [],
+        query_suffix: str = "", **kwargs: Any
     ) -> List[Dict]:
         """Run query through Searx API and returns the results with metadata.
 
         Args:
             query: The query to search for.
 
+            query_suffix: Extra suffix appended to the query.
+
             num_results: Limit the number of results to return.
 
             engines: List of engines to use for the query.
@@ -308,6 +348,10 @@ class SearxSearchWrapper(BaseModel):
             "q": query,
         }
         params = {**self.params, **_params, **kwargs}
+        if len(self.query_suffix) > 0:
+            params["q"] += " " + self.query_suffix
+        if isinstance(query_suffix, str) and len(query_suffix) > 0:
+            params["q"] += " " + query_suffix
         if isinstance(engines, list) and len(engines) > 0:
             params["engines"] = ",".join(engines)
         results = self._searx_api_query(params).results[:num_results]